One basic component of a semiconductor device is a transistor, commonly referred to as a FET. Various types of FET devices exist, and the function, composition, and use of FET devices varies. One type of FET device commonly used in semiconductor devices is a metal-oxide-semiconductor field effect transistor (MOSFET). MOSFET devices generally come in two distinct types, positive MOSFET (pMOS) devices, and negative MOSFET (nMOS) devices. Digital data processing devices may include a combination of pMOS and nMOS devices, which are arranged in a complimentary metal-oxide-semiconductor (CMOS) arrangement. Transistor size constraints in advanced semiconductor devices have required more compact transistor designs and topologies. One such design includes a fin-shaped FET (finFET). FinFETs may include multi-gate structures combined to provide scalable CMOS circuits for digital applications.
During processes of fabricating channel structures in the fins, strain can be introduced in the channel. The strain may be a physical or mechanical result of the materials used in fabricating the structure. Also, varying strain may be caused by variations in physical dimensions of the channel structures. Variations in strain parameters may affect performance of the device. The effects may be adverse, or may enhance the performance of the device, depending upon the device configuration and the value of the strain parameter. Some examples of channel layers or channel structure include horizontal nano-sheets (hNS) and horizontal nano-wires (hNW).
Source/Drain (SD) stressors used in prior fabrication processes become less efficient with scaling, due to smaller SD volume. Also, SD stressors are not easy to implement to achieve tensile stressed channels in nMOS devices. Processing flows with built in stressed layers as starting material, such as those using strained silicon on insulator (sSOI), etc., and processing flows using underlayer stressors like strain relaxed buffer (SRB), face serious difficulties in maintaining the stress through the fabrication flow, typically losing most of the initial stress. In particular, stress is lost during deep SD recess and/or fin cut, due to elastic relaxation. Unfortunately, the strain is not adequately recovered during SD epitaxial regrowth, and as a consequence, the resulting devices have little or no strain in the channel. A way around this problem for these flows is to eliminate the deep SD recess and use clad epitaxial material in the SD (i.e. add epitaxial layer on top of the fin structure on the SD, without previously performing a SD recess), however, this may result in non-optimal doping profiles.